Lake Victoria, one of the African Great Lakes, is a hotspot for Schistosoma mansoni¸ a major human parasite responsible for schistosomiasis (snail fever) that uses freshwater snails of the genus Biomphalaria as intermediate hosts. Past studies linked some Biomphalaria species with varying parasite compatibility, which impacts local transmission. Lake Victoria, according to experts, is home to two species: B. choanomphala and B. sudanica. But questions remained about the taxonomy of these species. Now researchers from the United Kingdom have discovered that molecular groupings are inconsistent with morphological divisions. The study, published in the journal PLoS ONE, was funded in part by the CONTRAST ('A multidisciplinary alliance to optimise schistosomiasis control and transmission surveillance in sub-Saharan Africa') project. CONTRAST received almost EUR 3 million in funding under the International Cooperation (INCO) Cross-cutting activity of the EU's Sixth Framework Programme (FP6).

Putting morphological and molecular variables in the spotlight, researchers from the University of Nottingham and the Natural History Museum, London in the United Kingdom found that molecular groupings are inconsistent with morphological divisions.

Their data show that habitat predicted morphotype, thus hinting that the various forms of Biomphalaria found in Lake Victoria are ecophenotypes of one species, that is, they are phenotypes resulting from environmental conditions and not from genetic expression.

The researchers recommend a change be made to the classification, proposing the names B. choanomphala choanomphala and B. c. sudanica.

'The desire to identify accurately the species of Biomphalaria in Lake Victoria is linked directly to the need for greater understanding of the transmission patterns of S. mansoni in the lake,' write the authors of the paper. 'Intestinal schistosomiasis is rife in communities living by the lakeshore, and by understanding the dynamics of the snails responsible for transmission it will be possible to identify possible exposure hot-spots, and direct treatment and education interventions to these areas.'

The team says an interesting finding was that several differences in the average measurements were significant between habitat types. 'Although causation is far from certain, this evidence could tentatively suggest that habitat might be a factor in driving the morphological plasticity seen in the dataset,' the authors write. 'Shell shape is known to be strongly environmentally determined in many snail species so it would not be difficult to imagine factors associated with habitat driving ecophenotypic variation in Biomphalaria in Lake Victoria.'

Policymakers could use the results of this study to improve our knowledge about exposure risk, and devise and implement better and more effective control initiatives.